Top 17 'Mental-Model-Stacking' Educational Apps to master for free for Making Smarter Decisions in 2025
Ever feel like you're drowning in information but starving for wisdom? You read articles, listen to podcasts, and scroll through endless feeds, yet when it's time to make a crucial decision, your mind feels... foggy. It's a common struggle in our age of information overload. We have access to all the data in the world, but not the frameworks to properly process it.
This is where mental models come in. Think of them as software for your brain—simple, powerful concepts that help you understand the world. Models like 'First Principles Thinking,' 'Second-Order Thinking,' or 'Inversion' are frameworks that cut through the noise and reveal the core of a problem. But here's the secret the world's sharpest thinkers know: the real magic isn't in knowing one or two models. It's in 'stacking' them.
Mental-model-stacking is the art of combining multiple frameworks to look at a situation from different angles, creating a rich, multi-dimensional understanding that leads to vastly superior decisions. It’s a concept I’ve seen thinkers like Charlie Munger and, closer to home, Goh Ling Yong, advocate for relentlessly. The good news? You don't need an expensive MBA or a library full of dusty books to start. In 2025, the best tools to build this superpower are sitting right in your pocket, and most of them are free.
Here are the top 17 educational apps you can master for free to start stacking mental models and making smarter decisions today.
1. Untools: Your Digital Encyclopedia of Thinking Frameworks
Untools isn't just an app; it's a curated gallery of high-impact thinking tools and frameworks. It cleanly categorizes models for problem-solving, decision-making, and systems thinking. If you’re just starting your journey, this is your ground zero. It presents each model with a simple explanation and a visual graphic, making complex ideas instantly digestible.
The real power of Untools is how it facilitates conscious stacking. Instead of relying on your default thinking patterns, you can browse its library and intentionally select a few models to apply to a problem. This deliberate practice is the first step toward making model-stacking an automatic habit. It’s like having a cognitive coach on call, ready to offer a new lens when you feel stuck.
Pro-Tip: Facing a difficult choice? Start with the "First Principles" model on Untools to break the problem down to its fundamental truths. Then, stack the "Second-Order Thinking" model on top to consider the long-term consequences of your potential solutions.
2. Notion: The Architect of Your Second Brain
Notion (and its excellent alternative, Obsidian) is less of an app and more of a universe for your thoughts. Its free tier is incredibly generous, allowing you to build a personal "Second Brain"—a digital extension of your mind. This is the ultimate playground for mental-model-stacking because you can create your own interconnected database of ideas.
You can create a page for each mental model you learn, complete with your own examples and insights. Then, using Notion's powerful linking feature, you can connect them. See a link between 'Occam's Razor' and 'Hanlon's Razor'? Link them. Realize that 'Circle of Competence' is crucial for applying 'First Principles'? Link them. Over time, you build a personal, visual latticework of knowledge that mirrors how your brain actually works.
Pro-Tip: Create a "Decisions" database in Notion. For every major decision, create a new entry and tag the mental models you used to arrive at your conclusion. This creates a powerful feedback loop for refining your thinking process.
3. XMind: The Visual Connector of Ideas
Mind mapping is, in itself, a powerful mental model for organizing thoughts. XMind's free version is a best-in-class tool for creating beautiful, functional mind maps. While Notion helps you build a structured database, XMind helps you explore the chaotic, creative connections between ideas in real-time.
When you're trying to stack models, a mind map is your canvas. Place your central problem in the middle. Then, create main branches for different mental models you want to apply—'Inversion,' 'Constraints,' 'Pareto Principle,' etc. As you explore each branch, you'll start to see unexpected connections and solutions emerge. It's a fantastic way to visualize how different frameworks interact and influence each other.
Pro-Tip: Use XMind for a "pre-mortem" analysis. Put "Project Failure" in the center and use models like the '5 Whys' and 'Inversion' (i.e., "What would we have to do to guarantee failure?") to map out all potential risks.
4. Farnam Street (Blog/Podcast as an "App"): The Latticework University
While not a traditional app, the Farnam Street (FS) blog and its "The Knowledge Project" podcast are an essential, free resource. Treat it like a university course in clear thinking. Adding their blog to your phone's home screen effectively turns it into an app you can access anytime. Shane Parrish and his team do an incredible job of deconstructing mental models and cognitive biases.
The value of FS is the depth and context it provides. It’s not just a dictionary of models; it’s a collection of stories, historical examples, and interviews with brilliant minds that show these models in action. This narrative approach helps embed the concepts in your memory far more effectively than a dry definition ever could.
Pro-Tip: Create a routine. Every Sunday, read one article from the FS archive. Write down the key model discussed and one personal or professional situation where you could apply it that week.
5. Khan Academy: The Bedrock of First Principles
You might think of Khan Academy as a tool for high school math, but it's one of the most powerful resources for mastering 'First Principles Thinking.' To break a problem down to its fundamental truths, you first need to understand those truths. Khan Academy offers free, world-class education on the foundations of physics, chemistry, economics, and logic.
Want to truly understand the energy industry? Don't just read business reports; take Khan Academy's course on thermodynamics. Trying to build a financial model? Master their lessons on compound interest and probability first. By strengthening your understanding of these core scientific and mathematical principles, you give yourself the raw materials to reason from the ground up, rather than by analogy.
Pro-Tip: Pick one industry or topic you're interested in. Spend 15 minutes a day on Khan Academy learning the most basic, foundational science behind it. You'll be amazed at the clarity this brings.
6. Brilliant.org: The Interactive Gym for Your Logic Muscles
Brilliant takes the foundational knowledge of Khan Academy and turns it into an interactive, problem-solving experience. While a full subscription is paid, its free daily challenges and course previews are fantastic for sharpening the quantitative and logical reasoning skills that underpin many mental models.
The app forces you to think actively, not passively. You learn concepts like 'Bayesian thinking' not by reading about them, but by solving puzzles that require you to apply them. This hands-on approach builds cognitive agility, making you faster and more flexible when you need to select and stack models under pressure.
Pro-Tip: Make the free daily problem a part of your morning routine. It's a 5-minute cognitive warm-up that trains your brain to look for elegant, logical solutions.
7. Anki: Forging Models into Your Subconscious
Anki is a free, open-source spaced repetition software (SRS). It's a flashcard app on steroids. Most people use it to memorize facts, but its true power lies in internalizing complex concepts until they become second-nature, intuitive tools. This is how you go from knowing about a mental model to using it automatically.
Create your own "Mental Models" deck. For each model, create a few cards. One card might ask for the definition. Another might ask, "In what situation is this model most useful?" And a third might present a problem where that model is the key to the solution. The SRS algorithm shows you the cards just as you're about to forget them, searing them into your long-term memory.
Pro-Tip: Don't just define the model. Create "antonym" cards. For example, a card could ask, "What is the opposite of Second-Order Thinking?" (Answer: First-order, short-term, reactionary thinking). This helps you understand the concept on a deeper level.
8. Pocket: Your Curated Library of Ideas
Pocket is a simple "read-it-later" app, but it's a critical component of your mental model toolkit. Our brains aren't great at learning on demand. When you stumble upon an insightful article during a busy workday, you can't give it the attention it deserves. Pocket lets you save it for a dedicated learning session.
This transforms your information consumption from a reactive trickle to a deliberate, focused practice. It allows you to gather raw materials from diverse sources—technology, history, psychology—and then find the patterns and underlying models connecting them. Much like my own approach, which I know resonates with readers of Goh Ling Yong's work, the goal isn't just to collect articles but to build an interconnected web of knowledge.
Pro-Tip: Use Pocket's tagging feature religiously. Tag articles not just by topic (#AI, #Finance) but by the mental models they illustrate (#Inversion, #AsymmetricBets). You'll soon have a personalized library for each of your favorite thinking tools.
9. Feedly: Your Personal Intelligence Agency
If Pocket is where you analyze content, Feedly is how you source it. Feedly is an RSS reader that lets you pull content from your favorite blogs, news sites, and journals into one clean feed. It puts you in control, replacing algorithm-driven social media feeds with sources you've personally vetted.
This allows you to practice the 'Circle of Competence' model. You can build feeds dedicated to your core areas of expertise, ensuring you stay at the cutting edge. But you can also create a "Serendipity" feed with sources from totally unrelated fields—like biology, art history, or poetry—to foster the cross-disciplinary thinking that is the hallmark of great decision-makers.
Pro-Tip: Don't just follow individuals. Use Feedly to follow specific scientific journals or niche industry publications. This helps you get closer to the primary sources of information, a key tenet of 'First Principles Thinking.'
10. Medium: The Modern Hub for Diverse Thought
Medium's free tier gives you access to a limited number of articles per month, but it's a treasure trove of well-articulated ideas. It's a platform where experts in a thousand different fields share their insights. It’s one of the best places online to discover new mental models or see old ones applied in novel contexts.
The key is to be an active, not a passive, reader. When you read a compelling article, don't just nod along. Ask yourself: What is the underlying mental model the author is using? Are they arguing from first principles? Are they highlighting a cognitive bias? Deconstructing the arguments of others is excellent practice for constructing your own.
Pro-Tip: Follow specific "Publications" on Medium, not just individual authors. Publications like Cantor's Paradise (for math and science) or UX Collective (for design thinking) offer a curated stream of high-quality, model-rich content.
11. TED: A Masterclass in Cross-Disciplinary Thinking
The TED app provides free access to thousands of short, powerful talks from every discipline imaginable. This is perhaps the most efficient way to get a crash course in a new field and absorb its core mental models. Listening to a neuroscientist, an economist, and an artist back-to-back trains your brain to look for connections between seemingly disparate fields.
This is the very essence of building a "latticework of mental models." A physicist might teach you about 'Entropy,' which you can then apply to understanding organizational decay. A biologist's talk on 'Ecosystems' can provide a powerful new model for thinking about market dynamics. TED is the ultimate source for these perspective-shifting ideas.
Pro-Tip: Use the "Surprise Me" feature. Let the app serve you a random talk. This intentional injection of randomness can break you out of your intellectual bubble and introduce you to models you'd never find otherwise.
12. Stoic: Journaling for Mental Clarity
The Stoic app provides guided journaling prompts based on the ancient philosophy of Stoicism—which is, essentially, a robust operating system of mental models for a good life. Models like the 'Dichotomy of Control' (focusing on what you can influence) and 'Premeditatio Malorum' (negative visualization) are built directly into the app's exercises.
Decision-making isn't just a logical process; it's an emotional one. This app helps you master the internal landscape. By journaling and reflecting, you become more aware of the cognitive biases and emotional reactions that can cloud your judgment. A clear mind is a prerequisite for effective model-stacking.
Pro-Tip: Use the "Evening Reflection" feature every night for a week. The guided questions help you analyze your day, identify where you acted emotionally versus rationally, and plan to do better tomorrow.
13. Forest: Gamifying Deep Work
At its core, Forest is a focus timer that helps you beat phone addiction. You set a timer, and if you stay off your phone, a virtual tree grows. If you exit the app, the tree withers. But it's more than that; it's a tool for practicing the mental model of 'Deep Work.'
Learning and applying mental models requires focused, uninterrupted thought. You can't stack second-order thinking on top of first principles if you're being distracted by notifications every 30 seconds. Use Forest to carve out dedicated "thinking time" to work on a specific problem or learn a new model from your Notion database.
Pro-Tip: Stack Forest with another app on this list. For example, set a 25-minute Forest timer to read an article in Pocket and take notes, creating an intentional, focused learning sprint.
14. Google Scholar: Your Gateway to Primary Sources
For making truly high-stakes decisions, you sometimes need to go beyond blogs and articles to the primary research. Google Scholar is a free search engine for academic literature. It’s your tool for applying the 'Go to the Source' mental model.
Learning to navigate and skim academic papers is a superpower. You learn to identify a paper's core argument, check its methodology, and evaluate the strength of its evidence. It also helps you use tools like 'Connected Papers' to see how ideas are linked and built upon in the scientific community, giving you a visceral understanding of 'Systems Thinking.'
Pro-Tip: When you hear a claim in the news like "a new study shows...," use Google Scholar to find the actual study. Try to read the abstract and conclusion. You'll quickly learn to spot the difference between media hype and scientific reality.
15. Elevate: The Cognitive Calisthenics App
Elevate (and similar brain-training apps like Lumosity) offers a free selection of games designed to improve cognitive skills like processing speed, focus, and brevity. Think of this as the physical conditioning required to be a mental athlete.
While these games won't directly teach you mental models, they sharpen the underlying tools you need to use them effectively. A game that trains you to quickly identify grammatical errors also trains your 'Attention to Detail.' A math game that forces quick estimations hones your sense of 'Scale' and 'Proportionality.' It’s the daily calisthenics that makes the heavy lifting of decision-making easier.
Pro-Tip: Focus on the "Writing" and "Speaking" games in Elevate. The ability to articulate your thoughts clearly is a sign that you have truly grasped the mental models you're using.
16. Habitica: Gamifying the Habit of Thinking
Habitica is an app that turns your life into a role-playing game (RPG). You create an avatar, and by completing your real-life tasks and habits, you earn experience points and gold to level up. This brilliant use of behavioral psychology—a set of mental models in itself—can be harnessed to build your thinking routine.
Turn "learning" and "applying" mental models into daily quests in Habitica. Create a "Daily" task called "Review Anki Deck for 10 Mins." Create a "Habit" called "Apply Inversion to a Problem." By rewarding yourself for these cognitive actions, you're hacking your own motivation and making the process of becoming a better thinker fun and sustainable.
Pro-Tip: Create a custom "Reward" in Habitica, like "30 Minutes of Guilt-Free YouTube," that you can only "purchase" with the gold you've earned from completing your thinking-related habits.
17. Project Euler: The Deep End of Algorithmic Thinking
This one is for those who enjoy a serious challenge. Project Euler is a website (which can be used like an app) that presents a series of computationally intensive math problems. Solving them requires not just programming skill, but a deep understanding of logic, efficiency, and algorithmic thinking.
Working on these problems forces you to develop mental models related to 'Constraints,' 'Optimization,' and 'Scalability.' You learn to think about problems not just in terms of a single correct answer, but in terms of the most elegant and efficient path to that answer. This rigorous, systematic approach to problem-solving will bleed over into every other area of your life.
Pro-Tip: You don't have to be a coder to benefit. Read the first few problems and just try to map out the logic of a solution on paper. The act of structuring the problem is where 90% of the learning happens.
Your Toolkit for a Wiser 2025
The power isn't in any single one of these apps. It's in the personalized, interconnected system you build with them. Use Feedly and Pocket to gather ideas, Notion to connect them, Anki to internalize them, and Forest to find the focus to apply them.
Start small. Pick just one or two apps from this list that resonate with you. The goal isn't to master all 17 overnight. The goal is to begin the process—the lifelong, rewarding process of building a latticework of mental models in your mind. By doing so, you'll equip yourself not just with answers, but with a superior way of thinking that will serve you for years to come.
Now, I want to hear from you. Which app will you try first? And what’s one mental model you’re excited to master in 2025? Share your thoughts in the comments below
About the Author
Goh Ling Yong is a content creator and digital strategist sharing insights across various topics. Connect and follow for more content:
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